The proposed project is an investigation of the synthesis and assembly of eucaryotic cell plasma membrane proteins. Particular attention will be paid to determining how integral glycoproteins and peripheral proteins interact in a coordinated manner as the membrane is synthesized. We shall investigate the glycoproteins (e.g. band 3 and glycophorin) and peripheral proteins (e.g. spectrin) of the erythrocyte. These proteins, which are made by erythrocyte precursors, are also synthesized by Friend Leukemic (FL) cells when they progress along the erythroid differentiation pathway in a semi-synchronous manner after treatment with inducing agents. Immune techniques, using antisera against purified erythrocyte membrane proteins will be identified by plasma membrane fractionation. Pulse labelling of cells throughout the process of differentiation should show the sequence of onset and cessation of synthesis of these membrane proteins and may reveal a process of coordinated gene expression. One approach to the investigation of the switch on and off of membrane protein synthesis will involve isolation of mRNA form differentiating FL cells and its translation in a heterologous system. We shall also analyze the products of in vitro translation for the synthesis of precursor proteins suggesting the presence of possible signal sequences. Finally, we shall investigate how peripheral proteins attach to the cytoplasmic surface of the plasma membrane and how they interact with the transmembrane glycoproteins and control their distribution in the plane of the membrane.